Immunotherapy has shown promise as an important new approach to the treatment of malignancy. Several immune effector cells and molecules facilitate tumor cell destruction. The goal of this project is to identify tumor antigens recognized by cytotoxic T cells. We will accomplish this goal through the isolation of cDNA clones derived from a tumor cell libraries, which encode these antigens. The cDNA clones will be identified using the specificity of cloned cytotoxic T lymphocytes (CTL) isolated from tumor-bearing animals. Two weakly immunogenic murine tumors, CT26, (a colon adenocarcinoma), and MCA 106 (a fibrosarcoma) will be studied. Because the tumors are weakly immunogenic, the precursor frequency of tumor reactive T cells will be low. They will be increased through transfection of an allogeneic class I major histocompatibility complex (MHC) gene directly into tumor cells in vivo; a technique developed in this laboratory. Treatment of H-2b or H-2d tumors with the H-2Ks gene but not a control gene generates a cytolytic response to the allogeneic MHC protein expressed on transformed cells, mediated by Lyt2+ CTL. More importantly, the H-2Ks gene induces an immune response to previously unrecognized antigens present on unmodified cells. This immune response attenuates tumor growth and in some cases results in complete regression of established tumors. T cells induced by gene transfer of H-2Ks directly into poorly immunogenic tumors will be cloned and selected for reactivity to parental tumor cells. The cloned cells will be used to screen a tumor cDNA library expressed in syngeneic, transformed B cell lines. Candidate cDNA clones will be identified, cloned and sequenced. They will then be analyzed for their ability to induce immune reactivity and to determine whether their overexpression can lead to enhanced immune recognition. Analyses of these tumor antigens will enhance the understanding of molecular changes in neoplastic cells that provoke immunity. In addition, identification of these tumor antigens may be useful in the development of specific immunotherapy of malignancies, including tumor vaccines.